1. Field of the Invention
The present invention relates to gas flow rate control devices and brazing devices, and more particularly to an automatic brazing device for brazing, soldering, and the like, to join metal materials, ceramics, etc. using brazing wire having a melting point lower than that of the joined metals.
2. Description of the Background Art
As is disclosed in Japanese Patent Laying-Open No. 63-84761, a conventional automatic brazing device has a structure for brazing while moving a brazed material fixed in a certain position. Since it controls the amount of heating by the valve switching system, the control is made in steps even if the number of valves is increased. Furthermore, the ratio between combustible gas and burning-supporting gas is liable to become unstable due to variation in pressure of gas sources.
An automatic brazing device which takes in positional information and performs image processing for robotization is proposed in Japanese Patent Laying-Open No. 61-126968.
Also, an automatic brazing device which image-processes the temperature of a brazed part for robotization is proposed in Japanese Patent Laying-Open No. 7-88639.
In the above-described conventional system in which the heating amount is controlled by switching several passages with previously adjusted flow rates, it is necessary that an expert should repeatedly adjust the flow rate using a test piece in order to heat an object to the most suitable brazing temperature. Even after the flow rate is properly adjusted, a variation of the initial pressure of a gas source causes a change in state of flames of a burner and then the most suitable brazing temperature can not be obtained, which causes inferior brazing.
While the flow rate is controlled with a mass-flow valve in recent years, ideal reducing flame is not obtained if the flow rate ratio between combustible gas and burning-supporting gas changes, which also causes inferior finish of brazing.
Although the robotization for improving precision by image-processing positional information and temperature information does improve the brazing precision, it is so expensive that it is not suitable for automation of brazing of such mass-production parts as are positioned with jigs.
However, there have been strong demands for production of many types of conventional automatic brazing machines which achieve positioning with jigs, where it is necessary that experts set the heating amount and timing of supply of brazing wire by repeating tests on the basis of their brazing experiences. Accordingly, setting the conditions not only requires test pieces but also requires stopping operation of the automatic brazing machine in a long time.
Furthermore, there is also a social problem that such skilled workers as have experiences and ability enough to judge heating conditions and set timing for supply of brazing wire are chronically lacking due to the facts that such skilled workers are becoming older and that young workers are not willing to succeed to this technique.